Semiconductor chips or wafers are used in many applications, including as processor chips for computers, and as integrated circuits and as flash memory for hand held computing devices, wireless telephones, and digital cameras. A common circuit component of semiconductor chips is the transistor. In ULSI semiconductor chips, a transistor is established by forming a polysilicon gate stack on a silicon substrate, and then forming a source region and a drain region in the substrate beneath the gate stack by implanting ion dopants into the areas of the substrate that are to become the source and drain regions. This generally-described structure cooperates to function as a transistor.
To shield the gate from the ions that are implanted to establish the source and drain regions, a photoresist mask is deposited over the areas sought to be shielded prior to ion implantation. Ions are then implanted in the areas between adjacent masked areas, often using what is referred to as "high aspect ratio" implantation in which the ions are directed almost vertically against the unshielded areas. High aspect ratio implantation is increasingly used mainly because the resist mask dimensions (i.e., a high aspect ratio space region) increasingly are smaller than they have been, to facilitate establishing more components on smaller chips. While for illustration purposes the above discussion considers ion implantation and photoresist gate masking in the transistor context, it is to be understood that the present invention is more widely directed to ion implantation in general.
It happens that the photoresist mask regions are formed with rectangular profiles. As understood herein, during ion implantation the top shoulders of the rectangular photoresist mask regions can block portions of the ion beam, particularly when a high aspect ratio is used to implant the ions. The present invention, having recognized the above-noted problem, provides the below-disclosed solutions, which also enhance device scaling in terms of process capability, since the present invention efficiently addresses any implantation process that requires high aspect ratio implantation.